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xu, c,1 Brown and Heise: Carbon Dioxide Assimilation 3 
VAN AMSTEL’S WORK ON ELODEA 
An attempt has been made by van Amstel *® to determine the 
effect of temperature on the assimilation of carbon dioxide, when 
light is not a limiting factor. The plant used was Elodea. From 
experiments performed at temperatures of 24° and 36° C. with 
various intensities of light, van Amstel concluded that increasing 
the light beyond 2,000 Hefner-candles had no effect on the rate 
of assimilation. 
A series of experiments was then performed with a light 
intensity of 2,482 Hefner-candles and temperatures of 24°, 36.5°, 
40°, 42°, and 45°. At 36.5° the injurious effects of high tem- 
peratures apparently had not set in, but they were very evident 
at temperatures above 40°. From the curve showing the assimi- 
lation of carbon dioxide with increasing temperatures, van Amstel 
obtained a value of 1.26 for the temperature coefficient between 
24° and 34°. 
Concerning this coefficient she says: 
Now, at such temperatures for most of the physiological prucesses a 
higher temperature-coefficient is found. As a rule this even amounts to a 
value between 2 and 3, as in most chemical processes. By this circum- 
stance it becomes very improbable that we really did determine the velocity 
of the assimilation-process itself. 
‘Her chief reason for the above statement apparently is found. 
in the deviation of the temperature coefficient from the van’t. 
Hoff ratio. Since, as we have shown, it is to be expected that 
the coefficients of photosynthesis are low, her objection fails. As: 
a matter of fact, her experimental data show remarkably good 
agreement with one another, as is shown in Table I, in which we 
have added to the data in her summary * the corresponding tem- 
perature coefficients. In this and all succeeding determinations 
of temperature coefficients the following formula, given by 
Kanitz,” has been used: 
log Q,,.=10 (log K,—log K,) 
t.—f. 
in which oes 
@,,=temperature coefficient for an interval of 10° C. 
K,=rate observed at temperature t, 
K,=rate observed at temperature ¢,. 
* Van Amstel, J. E., On the influence of temperature on the CO--assimila- 
tion of Helodea canadensis, Rec. Trav. Bot. Neérl. 13 (1916) 1-29. 
* Op. cit. 25. 
* Quoted by Denny, F. E., Bot. Gazette 62 (1916) 156. 
